Visible-Light-Driven α-Allenylic C-O Bond Cleavage and Alkenyl C-S Formation: Metal-Free and Oxidant-Free Thiolation of Allenyl Phosphine Oxides

A visible-light photoredox cleavage of alpha-allenylic C-O bond and alkenyl C-S formation is disclosed for the first time. The thiolation of allenyl phosphine oxides with diaryl disulfides occurs smoothly in metal-free and mild conditions, affording novel S,P-bifunctionalized butadienes with moderate to excellent yields. Mechanistic studies explain the cleavage of a C(sp(3'))-O(Ar) bond in initiating a key alkenyl radical intermediate.